Wild bees of Grand Staircase-Escalante National Monument: richness, abundance, and spatio-temporal beta-diversity Olivia Messinger Carril1, Terry Griswold2, James Haefner3 and Joseph S. Wilson4 1 Santa Fe, NM, United States of America 2 USDA-ARS Pollinating Insects Research Unit, Logan, UT, United States of America 3 Biology Department, Emeritus Professor, Utah State University, Logan, UT, United States of America 4 Department of Biology, Utah State University - Tooele, Tooele, UT, United States of America ABSTRACT Interest in bees has grown dramatically in recent years in light of several studies that have reported widespread declines in bees and other pollinators. Investigating declines in wild bees can be difficult, however, due to the lack of faunal surveys that provide baseline data of bee richness and diversity. Protected lands such as national monuments and national parks can provide unique opportunities to learn about and monitor bee populations dynamics in a natural setting because the opportunity for large-scale changes to the landscape are reduced compared to unprotected lands. Here we report on a 4-year study of bees in Grand Staircase-Escalante National Monument (GSENM), found in southern Utah, USA. Using opportunistic collecting and a series of standardized plots, we collected bees throughout the six-month flowering season for four consecutive years. In total, 660 bee species are now known from the area, across 55 genera, and including 49 new species. Two genera not previously known to occur in the state of Utah were discovered, as well as 16 new species records for the state. Bees include ground-nesters, cavity- and twig-nesters, cleptoparasites, narrow specialists, generalists, solitary, and social species. The bee fauna reached peak diversity each spring, but also experienced a second peak in diversity in late summer, following monsoonal rains. The majority of GSENM's bees are highly localized, occurring in only a few locations throughout the monument, and often in low abundance, but consistently across the four years. Only a few species are widespread and super-abundant. Certain flowering Submitted 12 March 2018 Accepted 3 October 2018 plants appear to be inordinately attractive to the bees in GSENM, including several Published 7 November 2018 invasive species. GSENM protects one of the richest bee faunas in the west; the large Corresponding author elevational gradient, incredible number of flowering plants, and the mosaic of habitats Olivia Messinger Carril, are all likely contributors to this rich assemblage of bees. [email protected] Academic editor Chris Cutler Subjects Biogeography, Conservation Biology, Ecology, Entomology Additional Information and Keywords Bee declines, Pollinators, Conservation, National monuments, Native bees, Pollination Declarations can be found on ecology page 16 DOI 10.7717/peerj.5867 INTRODUCTION Distributed under Creative Commons Public Several recent analyses have concluded that certain species of wild bees may be in decline Domain Dedication (e.g., Bartomeus et al., 2013; Goulson et al., 2015; Potts et al., 2010). Whether these declines OPEN ACCESS are widespread across the more than 20,000 species found in the world is unknown How to cite this article Carril et al. (2018), Wild bees of Grand Staircase-Escalante National Monument: richness, abundance, and spatio-temporal beta-diversity. PeerJ 6:e5867; DOI 10.7717/peerj.5867 (Ghazoul, 2015). Such a decline would pose a significant threat to both natural ecosystems and agricultural communities, as bees are the primary pollinators of most of Earth's flowering plants (Ollerton, Winfree & Tarrant, 2011). Documenting the extent of declines both across populations of disparate bee taxa, and across widely differing ecosystems, however, has proven difficult for many reasons. First, native bees vary naturally in population size from year to year (Williams, Minckley & Silveira, 2001; Wilson, Messinger & Griswold, 2009), making upward or downward trends difficult to establish without multiple consecutive years of data (Lebuhn et al., 2013). Second, bee communities are often comprised of a few common species and many rare species (e.g., Russo et al., 2011; Winfree et al., 2015), requiring that an inordinately large number of specimens be collected in order to document the majority that are present (Russo et al., 2015). Third, there are relatively few historic records documenting bee ranges (Gibbs et al., 2017). With so little data about the historic size of bee populations, it is difficult to demonstrate whether current numbers indicate an improvement or a deterioration in bee health. Few standardized bee collections were made prior to the last two decades (Bartomeus et al., 2013; Biesmeijer et al., 2006), so there are few baseline data points against which to measure present-day bee population sizes. Moreover, those few standardized collections that are older than twenty years are often in areas where the landscape has been significantly altered, so that collection events today may be sampling a much different habitat, from a bee's perspective (Biesmeijer et al., 2006). Protected lands, such as monuments and parks, provide an exceptional opportunity for monitoring bee populations and thoroughly documenting the presence and abundance of a bee fauna for a large area. As there is no mandate for multiple use, national monuments and national parks seldom experience large-scale, unnatural changes across a landscape (Acrygg et al., 2013; Stein, Scott & Benton, 2008), and are less affected by some of the potential threats to native bees, including pesticides and fertilizers (Roulston & Goodell, 2011; Woodcock et al., 2017), conversion to agricultural or otherwise developed lands (Forrest et al., 2015; Palma, 2015), competition with honey bee hives (Cane & Tepedino, 2017), and habitat fragmentation (Howell, Alarcon & Minckley, 2017; Steffan-Dewenter, 2003). They provide a valuable natural laboratory in which to conduct standardized collections, that allows for the resampling of an area over long periods to observe trends in bee populations. Finally, they provide a spotlight for the organisms within. Through outreach and education, monuments and parks enlighten millions of visitors each year about the creatures they protect, and the value of those creatures for ecosystem function (Fancy, Gross & Carter, 2009). We conducted a large-scale, multi-year inventory of the bee fauna of one such area, Grand Staircase-Escalante National Monument (GSENM), which is a large area of protected land that, until recently, incorporated nearly 1.9 million acres of the Colorado Plateau in south-central Utah. While the monument is dominated by cold-desert plant communities, plants associated with warmer ecoregions occur at its southern and western extents. The region includes a diverse flora, with many endemic species (Fertig, 2005). Elevations in the monument range from 1,356 to 2,316 m, and encompass stands of aspen (Populus tremuloides), ponderosa (Pinus ponderosa), pinyon (Pinus spp.), juniper (Juniperus spp.), blackbrush (Coleogyne ramosissima), sagebrush (Artemisia spp.), grasslands, mixed desert Carril et al. (2018), PeerJ, DOI 10.7717/peerj.5867 2/29 scrub, meadows, and riparian zones. Temperatures range annually from −11 ◦C to 38 ◦C. Most precipitation occurs in the form of summer rainfall (average: 13.5 cm across the four years of our study, 2000–2003) with monsoonal weather events, but snow is also common throughout the monument from November through March (average across the years of the study: 11.7 cm) (Utah Climate Center, 2001–2005: https://climate.usu.edu/). Our study of GSENM used standardized bi-monthly sampling in one-hectare plots, supplemented by opportunistic collections, in order to determine the richness and diversity of bees in this protected area, assess short and long-term population fluctuations in bee species, as well as associate bees with habitat types. Prior to our study, knowledge of the fauna was limited to only 20 collector-days of sampling for the monument, and all were along major roads (Griswold, Parker & Tepedino, 1998). Our study provides an example of the usefulness of national monuments and parks for scientific studies of insects whose populations are difficult to quantify. Eventually, our research will result in additional publications on the spatial and temporal drivers of bee diversity on this landscape. For this particular paper, our focus is on documenting, summarizing, and broadly characterizing the diverse and unique bee fauna protected by GSENM. Specifically, we describe (1) the bee diversity, including new range boundaries and a summary of known life history traits, (2) spatial patterns, (3) seasonal patterns, and (4) floral relationships of the bee assemblage. Finally, we compare the diversity and composition of GSENM's fauna with other known bee assemblages, and consider this community in the context of western bee distributions. MATERIALS AND METHODS Field methods We collected bees in GSENM over a period of four years (2000–2003) using both opportunistic collections and standardized bi-monthly sampling in one-hectare plots (Fig. 1). This follows a protocol commonly used for bee studies, providing the opportunity for comparisons with other areas, past and future (LeBuhn, 2003). Across GSENM, and across the four years of the study, a total of 66 plots, each 50 m × 200 m were established (Table 1); 11 plots were sampled all four years, 12 plots were sampled for three years, 12 were sampled two years, and